Corneal Collagen Cross-Linking (CXL)
What is Keratoconus?
Keratoconus is a degenerative disorder in which structural changes to the cornea cause it to thin and change to a more conical shape than its normal gradual curve. Keratoconus can cause substantial distortion of vision, including multiple images, streaking and sensitivity to light. It is typically diagnosed in the patient's adolescent years and attains its most severe state in the twenties and thirties.
Keratoconus is not an uncommon disease with a prevalence ranging between 1 in 500 and 1 in 10,000. Most corneal specialists believe that the prevalence of this condition is actually higher than these estimates as current technology is now able to detect this disease at earlier stages and in more subtle forms. This is especially true of devices such as the Pentacam which can measure the cornea’s back surface.
As currently practiced by most surgeons, the procedure is relatively straightforward. Riboflavin (vitamin B2) eye drops are instilled after epithelial removal, as would be done routinely in preparation for performing photorefractive keratectomy (PRK). Riboflavin eye drops are then instilled in the eye for 30 minutes and anesthetic eye drops are used to make sure that the patient is comfortable during the procedure. After the riboflavin has saturated the cornea, the UV light source, calibrated to provide a steady irradiance of light is applied for 30 minutes in each eye.
For patients with corneas between 300-400 microns, a hypotonic riboflavin solution can be used to “swell” the cornea to above 400 microns prior to treatment. This protects the endothelium, lens, and other intraocular structures by ensuring only safe levels of UV penetrate to the deeper corneal layers. A “bandage” contact lens is sometimes placed in the eye immediately after surgery, and antibiotic and non-steroidal eye drops are then instilled. The patient is followed postoperatively until the epithelium is intact, (generally 2-6 days) and then refractions, topography and other measurements are monitored over the ensuing months and years.
Who is a Candidate for CXL?
As with many conditions, the earlier the patient is treated, the better the results. In some countries, CXL is used in patients as young as 10 years old who are found to have forme fruste (pre-clinical) or frank (clinical) keratoconus. This first line treatment makes it much less likely that these patients will develop severe irregular astigmatism and progress to require corneal transplantation. It appears to be possible to actually prevent the development of keratoconus in some patients with pre-clinical signs of keratoconus if CXL is performed early.
Some inclusion criteria for our study are:
- Age 12 or older
- Thinnest corneal pachymetry of 300 microns
- Forme fruste or clinical KCN on topography
- No more than moderate or mild apical corneal scarring
- Pellucid marginal degeneration
- Post-LASIK ectasia
- Some post-Radial Keratotomy (RK) patients
Treatment for Individuals with clinical keratoconus
Patients who already have developed clinical keratoconus can also benefit from CXL treatment. Roughly, 60-70% of patients have significant improvement in their vision in spectacles. It has been our experience that we can usually get patients to move one “step” up what we refer to as the “vision correction spectrum’. In other words, if they are intolerant of their rigid contact lenses and are headed towards a corneal transplant, we can often avoid transplantation and get them back more safely and comfortably into their contact lenses. If they are doing well in rigid lenses, we can sometimes get them into soft lenses and if they are wearing soft lenses well, we are often able to provide better vision with glasses.
We are actively enrolling patients in a multicenter CXL investigational study. Our results have been similar to those of europeanCurrent diagnostic criteria for enrollment include keratoconus (both clinical and pre-clinical forms), pellucid marginal degeneration, post-LASIK ectasia and some post-Radial Keratotomy (RK) patients. Patients must also be 12 or older and their thinnest corneal measurement must be 300 microns or more. We look forward to expanding our indications for CXL to bullous keratopathy and corneal ulcers7in the near future.
Because more and more patients with these corneal conditions are now seeking information about cross-linking and becoming interested in pursuing this option we have provided (see below) some questions and answers that we have found very helpful in our discussions with patients about this treatment. Some examples that we have found helpful with CXL patients